(1) Field of the Invention
The present invention relates to a semiconductor device suitable for use in a semiconductor optical amplifier applicable to, for example, an optical communication system.
(2) Description of the Related Art
Following the recent increasing demand for communication, the wavelength division multiplexing communication system (WDM communication system) is being developed, which will enable large-capacity transmission through one optical fiber by multiplexing plural signal light waves of different wavelengths.
As an optical amplifier used in such an optical communication system, a semiconductor optical amplifier (SOA) having a wide wavelength band, compact, and capable of a low-power consuming operation is a promising one.
On the other hand, the application range of a large-capacity, high-speed photonic network is spreading to a metro access system close to subscribers. A photonic network applied to a metro access system has a flexible network configuration using an optical add drop multiplexer (OADM) etc.
An optical amplifier used in such a network system is required to be capable of carrying out an automatic gain control (AGC) and/or an automatic power control (APC) against the variations in the number of wavelengths to be multiplexed and the variations in the intensity of light to be input.
L. J. Christiansen et al. “2R Regeneration in Concatenated Semiconductor Optical Amplifiers and Electroabsorbers.” European Conference on Optical Communications, September 2004 (hereinafter, referred to as Document 1) and Filip Ohman et al. “Semiconductor Devices for All-Optical Regeneration” ICTON 2003, We. B. 4, p. 41-46 (hereinafter, referred to as Document 2) have disclosed a proposal that an optical amplification region (SOA) and an electric field absorption region (EA; electro-absorber) are provided and the SOA is used under forward bias and the EA is used under backward bias.